There are a reverse transcriptase inhibitor and a protease inhibitor as the remedies for the acquired immune deficiency syndrome (AIDS) induced by infection with human immunodeficiency virus (HIV) However, the therapeutic effects are lost by appearance of drug-resistant HIV variants (SAISHIN IGAKU, Vol. 53, No. 9, 2031 (1998)). Therapy by the combined use of these drugs is complicated due to a number of requirements to be followed. In addition, there are many drugs to be administered and some of them exhibit various side effects (NIKKEI SCIENCE, Oct. 29 (1998)). In particular, a protease inhibitor, which requires a complicated method of administration and has a risk of involving various side effects, is known to increase the probability of inducing production and selection of resistant strains unless almost 100% of a required dose is administered (Molecular Medicine, Vol. 36, No. 9, 1012 (1999)).
Development of vaccines has been undertaken in view of the past experiences in which many viral diseases were exterminated or significantly reduced by vaccines. However, the use of vaccines in HIV is thought to be very difficult due to frequent occurrences of HIV variants (NIKKEI SCIENCE, October 42 (1998)).
As mentioned above, several compounds exhibiting anti-HIV effects have been reported. However, development of a novel antiviral agent having excellent antiretroviral activity, capable of withstanding expression of resistance, being free from toxicity and side effect, and capable of being subjected to a long use has been strongly desired.